Most white LED light bulbs use indirect excitation of phosphors from UV LED's similar to a fluorescent light bulb. If you look closely at the actual LED you will see a small dome of yellow colored material which is the phosphorous material. They change the phosphor mix to get different light color temperature, soft white (2600-3000 K), cool white (4000-6000 K), etc. Higher color temp bulbs have higher lumens output for same wattage but light is harsher blue-white color.
There is some variance in the emission from LED itself, variation in the quality of phosphorous material used, and big variability in the electronic driver circuitry. LED's need to be driven with a current source. The phosphorous material does degrade in visible light generation over time.
Worse efficiency is in many LED light strips that just have a ballast resistor in series with each individual LED from 12 vdc bus bar. Up to two thirds of applied power is heat in the ballast resistors. Some string strip LED's are series connected, like some Christmas tree light strings. These can be fed from an electronic ballast that provides the current source to the string. Downside is if one LED blows out whole string goes out.
For most normal house LED light bulbs, the electronic ballast is usually the weak link. They are usually the cause of premature failure of LED light bulb. Most use a simple rectifier-electrolytic filter capacitor from AC mains to feed a DC to DC current source converter. The electrolytic filter capacitor is usually the weak link in the electronic ballast. Many LED bulb electronic ballasts cannot be placed on a light dimmer so you need to carefully check the box labeling to see if a particular LED bulb can be placed on a dimmer. The ballast design is different for a dimmable LED bulb.
The simple rectifier-filter capacitor for AC to high voltage DC conversion gives them a poor power factor caused by high, short period current crest factor. Typically around 0.65 equivalent power factor. If you measure the AC current and multiply it by AC voltage you will get a volts x amps number that is over 1.5 times the bulb's wattage rating.
When running from a battery powered AC inverter, inverter losses are based on output current load so a poor power factor load creates higher inverter losses although for a small wattage LED it is not very much additional loss.
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